1. Field of the Invention
The present invention relates to a lens barrel including a cam ring and a rotational ring. The cam ring moves along an optical axis direction while rotating about the optical axis by rotation of the cam ring.
2. Description of the Related Art
A type of lens barrel including a cam ring and a rotational ring wherein the cam ring moves along an optical axis while rotating about the optical axis by rotation of the cam ring is well-known in the art. In this type of lens barrel, the rotational ring is positioned around the cam ring. This arrangement has been a cause of increasing the diameter of the lens barrel. However, it cannot be said that miniaturization of such a type of lens barrel has been extensively studied.
The present invention provides the aforementioned type of lens barrel which has structure making it possible to miniaturize the lens barrel, especially the diameter thereof.
For example, a lens barrel is provided, including a cam ring which is rotated about an optical axis to move at least one lens group in the optical axis direction via at least one first cam groove formed on an inner peripheral surface of the cam ring, and a rotational ring which transfers a rotational motion to the cam ring. The rotational ring includes at least one rotation-transmission arm extending in the optical axis direction. The cam ring includes at least one bottomed engaging recess which is formed on an outer peripheral surface of the cam ring, and in which the rotation-transmission arm is slidably inserted to be movable in the optical axis direction. One and the other of the rotation-transmission arm and the engaging recess include a guide groove which extends parallel to the optical axis and a guide projection which is engaged in the guide groove, the rotational ring transferring rotational motion thereof to the cam ring via engagement of the guide groove with the guide projection.
The lens barrel can further include a first ring positioned around the cam ring to be movable in the optical axis direction. The cam ring can include at least one second cam groove formed on an outer peripheral surface of the cam ring to move the first ring in the optical axis direction by rotation of the cam ring. The engaging recess is formed so as not to interfere with the second cam groove.
It is desirable for the second cam groove to be formed on the cam ring to extend firstly in a forward direction with respect to the optical axis, toward a front side of the cam ring, and subsequently extend back in a rearward direction with respect to the optical axis, toward a rear side of the cam ring so as to define a substantially V-shaped profile. The engaging recess of the cam ring is positioned behind the second cam groove in the optical axis direction.
It is desirable for a front end of the engaging recess of the cam ring to be positioned immediately behind a frontmost peak portion of the V-shaped profile of the second cam groove in the optical axis direction.
It is desirable for the guide projection to be formed along an extension line which extends parallel to the optical axis through a frontmost peak portion of the V-shaped profile.
The cam ring can include an outer flange formed on the cam ring to form a slot penetrating therethrough in the optical axis direction between the outer flange and a bottom radial surface of the engaging recess so that the rotation-transmission arm is slidably inserted in the engaging recess through the slot.
It is desirable for the cam ring to include an outer flange formed on the cam ring to form a slot extending in the optical axis direction between the outer flange and a bottom radial surface of the engaging recess so that the at least one rotation-transmission arm is slidably inserted in the engaging recess through the slot. The lens barrel can further include a second ring positioned around the first ring to be movable in the optical axis direction, a plurality of first bayonet prongs being formed on the second ring. The outer flange includes a plurality of second bayonet prongs which are engaged with the plurality of first bayonet prongs so that the cam ring and the second ring move together in the optical axis direction.
It is desirable for the cam ring to be movable in the optical axis direction with respect to the rotational ring. The guide groove and the guide projection are slidably engaged to be movable in the optical axis direction.
It is desirable for the rotational ring to be prevented from moving in the optical axis direction.
It is desirable for the lens barrel to further include a stationary barrel positioned around the cam ring and to include at least one cam-ring guiding cam groove formed on an inner peripheral surface thereof. The cam ring is rotated about the optical axis while moving in the optical axis direction in accordance with a profile of the cam ring guiding cam groove.
It is desirable for the rotational ring to be positioned in the stationary barrel so as to be rotatable about the optical axis without moving in the optical axis direction with respect to the stationary barrel.
The lens barrel can include a motor which generates the rotational motion, so that the rotational ring transfers the rotational motion from the motor to the cam ring.
The lens barrel can be a zoom lens barrel having a zoom lens optical system including the lens group, a focal length of the zoom lens optical system varying by rotation of the cam ring.
The rotation-transmission arm and the engaging recess can include a plurality of rotation-transmission arms and a corresponding plurality of engaging recesses, respectively. The plurality of rotation-transmission arms are engaged in the corresponding plurality of engaging recesses from the rear of the cam ring in the optical axis direction, respectively.
In another embodiment, a lens barrel is provided, including a rotational ring driven to rotate about an optical axis, a cam ring rotated about an optical axis by receiving a rotational motion of the rotational ring to move at least one lens group in the optical axis direction via at least one cam groove formed on an inner surface of the cam ring. The rotational ring includes a plurality of rotation-transmission arms extending in the optical axis direction. The cam ring includes a plurality of bottomed engaging recesses which are formed on an outer peripheral surface of the cam ring and in which the plurality of rotation-transmission arms are slidably inserted to be movable in the optical axis direction with respect to the plurality of engaging recesses, respectively. One and the other of the rotation-transmission arm and the engaging recess include a guide groove which extends parallel to the optical axis and a guide projection which is engaged in the guide groove, the rotational ring transferring rotational motion thereof to the cam ring via engagement of the guide groove with the guide projection.
The present disclosure relates to subject matter contained in Japanese Patent Application No. 2001-335562 (filed on Oct. 31, 2001) which is expressly incorporated herein by reference in its entirety.